Clostridium difficile is the major causative agent of hospital-acquired diarrhea and colitis. Recent studies indicate that neuropeptides participate in the pathophysiology of diarrhea and intestinal inflammation. The neuropeptide corticotropin-releasing hormone (CRH) is an important mediator of inflammatory responses. CRH has anti-inflammatory properties exerted via activation of the hypothalamic-pituitary adrenal (HPA) axis and release of glucocorticoids. Moreover, CRH released from peripheral inflammatory sites exerts direct pro-inflammatory effects. Recent results provide evidence for an important role of CRH and the HPA axis in intestinal inflammation in response to C. difficile toxin A. We will test the hypothesis that central CRH, via activation of the HPA axis and release of glucocorticoids, exerts anti-inflammatory effects on intestinal inflammation, whereas peripheral CRH augments diarrhea and colonic inflammation via binding to intestinal CRH receptors and activation of specific pro-inflammatory transcription factors. In aim 1 we will examine the involvement of CRF in toxin A-induced inflammation by assessing inflammatory and secretory changes in CRH -/- and control mice and comparing these change with circulating levels of ACTH and corticosterone. We will also examine whether glucocorticoid insufficiency alters the colonic inflammatory responses to toxin A in CRH deficient mice. In collaboration with Dr. Barry Wershil we will determine the pathophysiologic importance of CRH and its receptors in activation of mast cells in vivo using CRH deficient and mast cell deficient mice. In aim 2 we will identify the cells in the colon the express CRH receptors in both CRH deficient and normal mice before and after colitis and examine the functional significance of CRH receptors in the development of colitis. The importance of CRH and CRH receptors in human colitis will also be evaluated in fetal intestinal xenografts in collaboration with Dr. Tor Savidge. In aim 3 we will examine whether CRH-induced activation of transcription factors in colonic epithelial cells is involved in the mediation of the pro-inflammatory effects of CRH in the colon. Results from our studies will define the pathophysiology mechanisms by which colonic inflammatory responses are controlled through communication between the nervous, endocrine, and immune system and may provide information on novel therapeutic approaches for intestinal inflammation.